In this paper, we investigate a countermeasure of zinc oxide fumes exhaling from the metal melting shop of a casting plant. It is most effective to establish a local exhaust system by using a canopy hood for a plume containing a lot of fumes from a heat source, depending on the working condition, however, there are some difficult cases to cover a hood on a plume source. In such a case, though a push-pull ventilation would be effective to exhaust fumes, there are few design data on a three dimensional push-pull flows with mighty buoyancy. Therefore, the dimensions of push-pull system are decided after taking working conditions into consideration, and then, the push-pull flows are simmulated numerically in order to obtain appropriate push and pull velocities to exhaust plume containing zinc oxide fumes. Numerical calculations are performed by using SIMPLE method, provided that air density is handled as a variable. A real size of push-pull system is made based on the results of numerical calculations, and experiments are performed at the actual melting shop to confirm the effectiveness of the push-pull ventilation. As the results, it becomes clear that the plume can be kept sufficiently under contorol by the push-pull velocities obtained from numerical solutions and the actual plume flows agree well with the numerical results. From the above facts, we may conclude that the numerical method may be an effective measure to design a push-pull ventilation system.